Heat Radiation Sheet

ABSTRACT

Disclosed is a heat radiation sheet, including a thermoconductive adhesive layer, a thermal diffusion layer, an adiabatic adhesive layer formed on the thermal diffusion layer, and a graphite layer. The thermoconductive adhesive layer is formed by mixing a metal powder with a nonconductive resin adhesive, the thermal diffusion layer is formed of metal foil, and the adiabatic adhesive layer is formed by mixing a metal powder with a nonconductive resin adhesive. The heat radiation sheet is effective in that high-temperature heat generated from heat sources of various kinds of electronic appliances is rapidly absorbed by a thermoconductive adhesive layer and a thermal diffusion layer, and the absorbed heat rapidly spreads over the entire area of the heat radiation sheet, is stored, and is then slowly discharged to prevent the external temperature of the electronic appliance from rapidly increasing, preventing the deterioration of reliability attributable to the high-temperature heat.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a heat radiation sheet for discharging heat generated from various kinds of electronic components, such as optical components, power semiconductors, LEDs and the like, electronic and electric products, communication appliances or electronic appliances. More particularly, the present invention relates to a heat radiation sheet including a thermoconductive adhesive layer, a thermal diffusion layer, an adiabatic adhesive layer and a graphite layer, wherein high-temperature heat generated from heat sources of various kinds of appliances is rapidly absorbed, and the absorbed high-temperature heat is uniformly diffused and properly stored to delay the discharge of the high-temperature heat to the outside of an appliance, so that the cooling action of heat sources can be sufficiently performed, and it is possible to prevent the high-temperature heat from being rapidly discharged to the outside of the appliance.

2. Description of the Related Art

As the integration degree of an integrated circuit (IC) is increased due to the advancement of industry, various kinds of appliances, such as hybrid packages, multiple modules, closed integrated circuits (LEDs, etc.), electronic appliances and the like, become increasingly complicated, slim and small, and thus the amount of heat generated from various kinds of electronic components is also increasing.

Therefore, owing to the increase of heat generation, a technology for preventing the malfunction of an electronic component and the damage of an electronic component by effectively discharging heat in a narrow space has been considered as an important factor. Further, there has been a problem that, if efforts are focused on heat radiation, a large amount of heat can be externally detected because the temperature in the vicinity of an appliance increases. Further, owing to the improvement of heat radiation performance, since externally-detected temperature increases, users cannot conveniently use the appliance because of high-temperature heat, and may frequently misunderstand the malfunction of the appliance.

Thus, in order to effectively discharge heat from an electronic appliance, a natural graphite sheet having high conductivity, a copper foil, an aluminum heat sink, a metal sheet, a conductive sheet formed by compacting metal powder, or a resin sheet formed by mixing metal powder with resin is generally used as a heat radiation sheet. However, the resin sheet is problematic in that heat transfer is insufficient in a horizontal direction, and the metal sheet is problematic in that its workability is not efficient and in that horizontal thermal conductivity and vertical thermal conductivity simultaneously increase, so heat is rapidly transferred to the surface thereof, thus excessively increasing external temperature.

Further, the natural graphite sheet, as another heat radiation sheet, is advantageous in that it can exhibit an excellent cooling effect on a heat source of an electronic appliance because it has a horizontal thermal conductivity of 300 W/mk, but is problematic in that its flexibility is not good because it is a highly-compressed sheet and it cannot be formed into a thin film, causing the external temperature of the electronic appliance to increase.

Referring to examples of conventional graphite heat-radiation sheets, Korean Patent Registration No. 10-0755014 discloses a graphite heat-radiation sheet, which is characterized in that one side thereof is coated with a thermoconductive adhesive prepared by mixing a polydimethylsiloxiane resin and a silicon resin with a thermoconductive filler, and the other side thereof is coated with a methylmethacrylate-trialkoxysilane copolymer solution, so it easily adheres to a display product, its thermal conductivity is improved, and graphite powder does not blow. However, this graphite heat-radiation sheet is advantageous in that it exhibits an excellent cooling effect on a heat source, but is problematic in that high-temperature heat is excessively and locally discharged to the outside because it has excessively high vertical thermoconductivity.

Meanwhile, Korean Unexamined Patent Application Publication No. 10-2011-0094635 discloses a heat radiation sheet, which is manufactured by coating a graphite sheet with an adhesive having high thermoconductivity to improve thermal conductivity and by simplifying a laminating process and an adhesive coating process into a single process. However, this heat radiation sheet is advantageous in that the cooling effect of a heat source is improved because it has excellent heat radiation performance and thermal conductivity in a vertical direction, but is problematic in that the external temperature of an appliance excessively and locally increases.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been devised to solve the above-mentioned problems, and an object of the present invention is to provide a heat radiation sheet using latent heat, which is characterized in that it includes a thermoconductive adhesive layer directly attached to a heat source of an electronic appliance, a thermal diffusion layer for rapidly and widely spreading the heat absorbed from the thermoconductive adhesive layer, an adiabatic adhesive layer for absorbing the heat spread in the thermal diffusion layer and storing the absorbed heat, and a graphite layer for absorbing the heat supplied from the adiabatic adhesive layer and delaying the discharge of the heat to the outside, so that the high-temperature heat generated from heat sources of various kinds of electronic appliances is rapidly absorbed to exhibit an excellent cooling effect, and the discharge of the absorbed heat is delayed by diffusion and latent heat to prevent the external temperature of the electronic appliance from rapidly increasing, thereby greatly improving the reliability of a product.

In order to accomplish the above object, an aspect of the present invention provides a heat radiation sheet, including: a thermoconductive adhesive layer including a release paper attached on one side thereof; a thermal diffusion layer formed on the thermoconductive adhesive layer; an adiabatic adhesive layer formed on the thermal diffusion layer; and a graphite layer formed on the adiabatic adhesive layer, wherein the thermoconductive adhesive layer is formed by mixing metal powder with a nonconductive resin adhesive, the thermal diffusion layer is formed of metal foil, and the adiabatic adhesive layer is formed by mixing metal powder with a nonconductive resin adhesive.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is an enlarged sectional view showing a heat radiation sheet according to a first embodiment of the present invention;

FIG. 2 is an enlarged sectional view showing a heat radiation sheet according to a second embodiment of the present invention; and

FIG. 3 is an enlarged sectional view showing a heat radiation sheet according to a third embodiment of the present invention.

REFERENCE NUMERALS

-   10: release paper -   20: thermoconductive adhesive layer -   30,30′: thermal diffusion layer -   40,40′: adiabatic adhesive layer -   41,41′: latent heat material -   50: graphite layer

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The terms and words used in the present specification and claims should not be interpreted as being limited to typical meanings or dictionary definitions, but should be interpreted as having meanings and concepts relevant to the technical scope of the present invention based on the rule according to which an inventor can appropriately define the concept of the term to describe the best method he or she knows for carrying out the invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

FIG. 1 is an enlarged sectional view showing a heat radiation sheet according to a first embodiment of the present invention.

As shown in FIG. 1, the heat radiation sheet according to the first embodiment of the present invention includes a thermoconductive adhesive layer 20 having a release paper 10 on a lower side thereof, a thermal diffusion layer 30 formed on the thermoconductive adhesive layer 20, an adiabatic adhesive layer 40 formed on the thermal diffusion layer 30, and a graphite layer 50 formed on the adiabatic adhesive layer 40.

In this case, the release paper 10 and the thermal diffusion layer 30 are attached to each other by the thermoconductive adhesive layer 20, and the thermal diffusion layer 30 and the graphite layer 50 are attached to each other by the adiabatic adhesive layer 40.

Further, the release paper 10 serves to protect the thermoconductive adhesive layer 20 of the heat radiation sheet according to the present invention. Before the heat radiation sheet is attached to a heat source of an electronic appliance, the release paper 10 is removed from the thermoconductive adhesive layer 20 to directly attach the thermoconductive adhesive layer 20 to the heat source.

Further, the thermoconductive adhesive layer 20 is prepared by mixing metal powder with a general adhesive, and the adhesive may be an acrylic adhesive, a urethane adhesive, a polyamide adhesive, a silicone adhesive or the like. This thermoconductive adhesive layer 20 serves to slowly absorb high-temperature heat generated from a heat source and transfer the absorbed heat to the thermal diffusion layer 30. The thermoconductive adhesive layer 20 is prepared by mixing 20˜30 wt % of metal powder, such as nickel powder, silver powder or alumina powder, with 60˜70 wt % of an adhesive. In this thermoconductive adhesive layer, the metal powder absorbs the heat from the adhesive, which is a nonconductor, and then transfers the absorbed heat to the thermal diffusion layer 30.

Here, the content of the metal powder is determined for the purpose of rapidly absorbing the heat generated from the heat source. When the content thereof is too small, an endothermic effect becomes weak, and when the content thereof is too large, adhesivity becomes low.

In this case, it is preferred that the thickness of the thermoconductive adhesive layer 20 be 20˜50 μm. When the thermoconductive adhesive layer 20 is too thin, adhesivity becomes low, thus weakening the fixation to the heat source. Further, when the thermoconductive adhesive layer 20 is too thick, thermal conductivity becomes low, thus reducing the effect of cooling the heat source.

Meanwhile, the heat absorbed by the thermoconductive adhesive layer 20 is rapidly spread over a large area by the thermal diffusion layer 30 formed on the thermoconductive adhesive layer 20. It is most preferred that the thermal diffusion layer 30 be made of aluminum foil or copper foil. This aluminum foil or copper foil has very high thermal conductivity and is excellent in workability and economic efficiency.

It is preferred that the thickness of the thermal diffusion layer 30 be 10˜100 μm. When the thermal diffusion layer 30 is too thin, thermal diffusivity increases, but heat is excessively and rapidly transferred to the adiabatic adhesive layer 40 formed on the thermal diffusion layer 30, thus causing the local temperature around the heat source to increase. Further, when the thermal diffusion layer 30 is too thick, the problem of increasing the local temperature around the heat source can be solved, but thermal diffusion speed is too slow, thus reducing the effect of cooling the heat source.

Thus, the heat widely spread by the thermal diffusion layer 30 is transferred to the adiabatic adhesive layer 40 formed on the thermal diffusion layer 30. The adiabatic adhesive layer 40 is made of a mixture of an adhesive and metal powder. The adiabatic adhesive layer 40 serves to exhibit a latent heat effect of temporarily storing the heat spread through the thermal diffusion layer 40.

That is, the adiabatic adhesive layer 40 is prepared by mixing 75˜85 wt % of a nonconductive resin adhesive, such as an acrylic adhesive, an urethane adhesive, a polyamide adhesive or a silicone adhesive, with 15˜25 wt % of metal powder, such as nickel powder, silver powder or alumina powder. The adiabatic adhesive layer 40, similarly to the thermoconductive adhesive layer 20, includes a nonconductive resin as a main raw material, but includes a relatively small amount of metal powder. Therefore, the thermal conductivity of the adiabatic adhesive layer 40 is lower than that of the thermoconductive adhesive layer 20.

That is, since the adiabatic adhesive layer 40 has lower thermal conductivity than that of the thermoconductive adhesive layer 20 and the thermal diffusion layer 30, heat transfer is delayed. Consequently, the adiabatic adhesive layer 40 exhibits a latent heat effect of delaying the transfer of the heat generated from the heat source upwards.

Further, the heat spread and transferred upward by the metal powder in the adiabatic adhesive layer 40 is further spread and delayed by the graphite layer 50 to be finally transferred to a case of an electronic appliance.

In this case, it is preferred that the thickness of the adiabatic adhesive layer 40 be 20˜50 μm. When the adiabatic adhesive layer 40 is too thin, adhesivity becomes low, thus weakening the fixation between the thermal diffusion 30 and the graphite layer 50. Further, when the adiabatic adhesive layer 40 is too thick, thermal conductivity becomes low, thus excessively reducing the effect of cooling the heat source.

Here, the themoconductive adhesive layer 20 and the thermal diffusion layer 30 serve to rapidly absorb the high-temperature heat generated from the heat source to prevent the heat source from being overheated, and the adiabatic adhesive layer 40 and the graphite layer 50 serve to receive the absorbed heat and then slowly discharge this heat to the outside to prevent the external temperature of an electronic appliance from being rapidly and locally increased.

Further, the graphite layer 50 serves to absorb the heat having passed through the adiabatic adhesive layer 40 to delay the discharge of the heat to the outside. Since the graphite layer 50 has surface resistance at the level of 10⁴, the conversion of externally-absorbed energy into thermal energy and the influence of the thermal energy on temperature can be minimized.

It is preferred that the thickness of the graphite layer 50 be 20˜50 μm. When the graphite layer 50 is too thin, the effect of delaying heat radiation decreases. Further, when the graphite layer 50 is too thick, the effect of delaying heat radiation excessively increases, thus negatively affecting the cooling effect on the heat source.

Since the above-configured heat radiation sheet of the present invention effectively cools a heat source of an electronic appliance, similarly to a conventional heat radiation sheet, and stores the heat generated from the heat source and then slowly discharges the heat to the outside, it is possible to prevent the external temperature of the electronic appliance from being rapidly and locally increased, thus preventing users from misunderstanding the malfunction of the electronic appliance and preventing users from being inconvenienced when using the electronic appliance because of high-temperature heat.

Meanwhile, in the heat radiation sheet according to the second embodiment of the present invention, the adiabatic adhesive layer 40 is formed by mixing a foaming agent with the conventional adhesive and the metal powder and then foaming the mixture. Since the adiabatic adhesive layer 40 formed in this way has an extremely large number of pores in the surface and interior thereof, the adiabaticity thereof is improved, thus increasing the latent heat effect of storing heat in the pores.

Here, it is preferred that the foaming agent be included in an amount of 2˜5% based on the amount of a mixture of an adhesive and a metal powder. Since this adiabatic adhesive layer 40 has an extremely large number of pores, it has predetermined cushioning properties. The cushioning properties serve to protect the components and heat source of an electronic appliance from external impact.

Further, in the heat radiation sheet according to the third embodiment of the present invention, the adiabatic adhesive layer 40 is formed by mixing a latent heat material 41 or 41′ prepared by sintering stone powder with the adhesive and the metal powder. In this case, this adiabatic adhesive layer 40 formed in this way has excellent adiabaticity and exhibits an excellent latent heat effect due to the influence of the stone powder. It is preferred that the latent heat material 41 or 41′ be included in an amount of 5˜10% based on the amount of a mixture of an adhesive and a metal powder.

Moreover, in the heat radiation sheet according to the present invention, the thermal diffusion layer 30 and the adiabatic adhesive layer 40 may be formed in a multiple structure in order to improve a heat radiation effect and a latent heat effect. In this case, a first thermal diffusion layer 30 is formed on a thermoconductive adhesive layer 20 having a release paper 10, a first adiabatic adhesive layer 40 is formed on the first thermal diffusion layer 30, a second thermal diffusion layer 30′ is formed on the first adiabatic adhesive layer 40, a second adiabatic adhesive layer 40′ is formed on the second thermal diffusion layer 30′, and then a graphite layer 50 is formed on the second adiabatic adhesive layer 40′.

Owing to the multiply-structured thermal diffusion layers 30 and 30′ and adiabatic adhesive layers 40 and 40′, a latent heat effect as well as a heat absorbing effect and a heat radiation effect can be further improved, so that, users can slowly feel the heat generated from a heat source of an electronic appliance. Further, even when the electronic appliance is not used, the heat generated from the heat source thereof is slowly discharged, thus preventing users from misunderstanding the malfunction of the electronic appliance and preventing users from being inconvenienced when using the electronic appliance because of high-temperature heat.

As described above, according to the heat radiation sheet of the present invention, high-temperature heat generated from heat sources of various kinds of electronic appliances is rapidly absorbed by a thermoconductive adhesive layer and a thermal diffusion layer to prevent the performance and efficiency of the electronic appliance from being deteriorated by the high-temperature heat, and the absorbed heat rapidly spreads over the entire area of the heat radiation sheet, is stored, and is then slowly discharged to prevent the external temperature of the electronic appliance from rapidly increasing, thereby preventing the deterioration of reliability attributable to the high-temperature heat. In this case, when the high-temperature heat is discharged from the electronic appliance, consumers can be cautious about using the electronic appliance in case it has a malfunction, thus preventing the discharge of high-temperature heat and further improving the reliability of the electronic appliance.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 

What is claimed is:
 1. A heat radiation sheet using latent heat, comprising: a thermoconductive adhesive layer including a release paper attached on one side thereof; a thermal diffusion layer formed on the thermoconductive adhesive layer; an adiabatic adhesive layer formed on the thermal diffusion layer; and a graphite layer formed on the adiabatic adhesive layer, wherein the thermoconductive adhesive layer is formed by mixing a metal powder with a nonconductive resin adhesive, the thermal diffusion layer is formed of metal foil, and the adiabatic adhesive layer is formed by mixing a metal powder with a nonconductive resin adhesive.
 2. The heat radiation sheet of claim 1, wherein the thermocondutive adhesive layer is prepared by mixing 60˜70 wt % of at least one adhesive selected from the group consisting of an acrylic adhesive, a urethane adhesive, a polyamide adhesive and a silicone adhesive with 20˜30 wt % of at least one metal powder selected from the group consisting of nickel powder, silver powder and alumina powder.
 3. The heat radiation sheet of claim 1, wherein the adiabatic adhesive layer is prepared by mixing 75˜85 wt % of at least one adhesive selected from the group consisting of an acrylic adhesive, an urethane adhesive, a polyamide adhesive and a silicone adhesive with 15˜25 wt % of at least one metal powder selected from the group consisting of nickel powder, silver powder and alumina powder.
 4. The heat radiation sheet of claim 3, wherein the adiabatic adhesive layer is prepared by mixing a foaming agent with the nonconductive resin adhesive and the metal powder.
 5. The heat radiation sheet of claim 1, wherein the adiabatic adhesive layer is prepared by mixing a latent heat material prepared by sintering stone powder with the nonconductive resin adhesive and the metal powder.
 6. The heat radiation sheet of claim 1, further comprising another thermal diffusion layer and another adiabatic adhesive layer between the adiabatic adhesive layer and the graphite layer.
 7. The heat radiation sheet of claim 1, wherein the thermoconductive adhesive layer has a thickness of 20˜50 μm, the thermal diffusion layer is made of copper or aluminum and has a thickness of 10˜100 μm, the adiabatic adhesive layer has a thickness of 4˜50 μm, the graphite layer has a thickness of 20˜50 μm, and these layers are formed into a laminate. 